The present invention relates to a device and method for use in the sampling and analyzing of bodily fluids, such as blood or interstitial fluid, which prevents short sampling.
The management of many medical conditions requires the measurement and monitoring of a variety of analytes, e.g., glucose, in bodily fluids. Currently, the measurement of analytes in blood typically requires a venipuncture or finger puncture to obtain blood for sampling purposes. More recently, techniques for analyzing interstitial fluid components have been developed. Regardless of the bodily fluid tested or analytical method used, it is important that sufficient sample is collected in order to ensure adequate test results. In prior art methods, however, adequate sample collection is often a matter of trial and error.
It is therefore desirable to have a sampling and analyzing device giving a clear signal that adequate sample has been collected before the sampling device, e.g., a needle or other penetration device, is removed from the patient""s body. It is also desirable that such a device be suitable for hospital bedside and home use.
Capillary and wicking fill devices are well-known as sampling devices and as sensing devices. However, one of the deficiencies of the prior art is that there is either no cue, or only a user-reliant visual cue, to indicate whether the device is fully filled.
The present invention provides a device, and a method for making and using the device, for ensuring that a capillary or wicking fill device is fully filled. In particular, the invention is directed to, but not limited to, use with capillary or wicking action-filled electrochemical sensors.
In one embodiment of the present invention, a device for sampling a fluid is provided, the device including a pre-chamber having an interior surface and a first volume, the pre-chamber being capable of exerting a first capillary force, the device further including a sensing chamber in fluid communication with the pre-chamber, the sensing chamber having an interior surface and a second volume, the sensing chamber being capable of exerting a second capillary force, wherein the first volume is not less than the second volume, and wherein a differential exists between the capillary forces, the differential being sufficient to cause flow of fluid from the pre-chamber to substantially fill the sensing chamber. The differential in capillary forces can result from the first and second pre-chamber walls being spaced apart at distance greater than the distance between the first and second sensing chamber walls. The differential can also result from the surface roughness, defined as the actual surface area divided by the geometric surface area, of the pre-chamber being less than that of the sensing chamber. Use of one or more surface treatments, which can be the same or different, in one or both of the pre-chamber and sensing chamber can result in a differential capillary force. The surface treatment can include, for example, a hydrophilic or hydrophobic substance. Surface treatments can be selected from surfactants, block copolymers, hygroscopic compounds, ionizable substances, and mixtures thereof.
In a further embodiment, one or both chambers can include, for example, one or more materials which contribute to the capillary force, such as meshes, fibrous materials, porous materials, powders, and mixtures or combinations thereof. Where a mesh is used, a smaller mesh can be used in the pre-chamber than that used in the analysis chamber. The mesh can be made of polyolefin, polyester, nylon, cellulose, polystyrene, polycarbonate, polysulfone or mixtures thereof. Fibrous filling material such as polyolefin, polyester, nylon, cellulose, polystyrene, polycarbonate, and polysulfone, or other nonwoven or melt blown polymers can be used. The porous material can include, for example, a sintered powder or a macroporous membrane, the membrane including polysulfone, polyvinylidenedifluoride, nylon, cellulose acetate, polymethacrylate, polyacrylate, or mixtures thereof. The powder, which can be soluble or insoluble in the sample, can include, for example, microcrystalline cellulose, soluble salts, insoluble salts, and sucrose.
In a further embodiment, the device includes electrodes capable of use in an electrochemical cell, or a detector capable of detecting a condition wherein the pre-chamber contains a volume of fluid sufficient to substantially fill the sensing chamber. A glucose monitoring test strip can include the device.
In yet another embodiment of the present invention, a method is provided for ensuring that a sensing device is substantially filled with a sample of fluid including: providing a device as described above; contacting the device with the fluid for a sufficient period of time to allow the fluid to enter the pre-chamber in an volume equal to or greater than the volume of the sensing chamber; and allowing the sample to flow from the pre-chamber to the sensing chamber, such that the sensing chamber is substantially filled. The method can further include the step of determining presence or absence of an analyte in the sample, e.g., conducting a quantitative measurement or electrochemical measurement of the analyte. The analyte can include, for example, a substance such as glucose, lactate, cholesterol, enzymes, nucleic acids, lipids, polysaccharides, and metabolites. The sample can include, for example, a biological fluid, such as a body fluid of an animal or plant, e.g., interstitial fluid, blood, tears, expectorate, saliva, urine, semen, vomitus, sputum, fruit juice, vegetable juice, plant sap, nectar, and biological fluid-based food products. Non-biological fluids that can be tested include non-biological fluid-based food products or beverages, drinking water, process water, and water-based solutions.
In a further embodiment of the present invention, a method of manufacturing a device as described above is provided, the method including: forming an aperture extending through a sheet of electrically resistive material, the aperture defining a side wall of the sensing chamber; mounting a first thin layer to a first side of the sheet and extending over the aperture whereby to define a first sensing chamber end wall; mounting a second thin layer to a second side of the sheet and extending over the aperture whereby to define a second sensing chamber end wall in substantial overlying registration with the first thin layer, whereby the sheet and layers form a strip; removing a section of the strip which overlaps the sensing chamber and an edge of the strip whereby to define a notch; mounting a first covering layer to a first side of the strip and extending over the notch whereby to define a first pre-chamber wall; and mounting a second covering layer to a second side of the strip and extending over the notch whereby to define a second pre-chamber wall in substantial overlying registration with the first covering layer.
In a further embodiment, the first and second thin layers can include a first and second electrode layer, the electrode layers facing in towards the cell. The electrodes, which can substantially cover the aperture, which can be circular, can include, for example, a noble metal, e.g., palladium, platinum, and silver, optionally sputter coated. An adhesive can be used to adhere the electrode layers to the sheet, e.g., a heat activated adhesive.
In a further embodiment, the chamber contains a chemical for use in the sensing chamber, e.g., a reagent capable of undergoing a redox reaction with an analyte or a reaction product of the analyte. The chemical can be printed onto at least one wall of the sensing chamber, or contained in or on a support included in the sensing chamber. At least one of the sheet, thin layers, or covering layers can include, for example, polyethylene terephthalate. The second electrode layer can be mounted in opposing relationship a distance of less than 200 microns from the first electrode layer.